It's happened a few times but I figured it should be thrown out there..
Sometimes when clearing out more unoccupied planets from my scans I find good ones.. "A decent planet, unoccupied? Coloniiize!" Then I realize they were a scan share (thankfully ended up being for anybody)
Even though they show in the news feed, I'd like to suggest some kind of icon over planet image - or extra text under 'control' category (share timer, maybe?) so that you know it's a share/alert. I'm fully aware they show up in recently scanned. But if you're not going through 'recently scanned' there's not much way of knowing without getting to the planet window -> Actions.

If that proposition isn't for way.. I'd suggest moving the colonize button into Actions tab, to make it a bit more obvious on the fact that it's a share.

If neither of the two.. Add a timer under colonize button with "shared: " in front of, as a direct indicator that it's shared to you.

Definately would help

Not to mention you wouldn't end up wasting Star Chart Purgers by accident.

+1
this is rather needed.